Chapter 20/21

Question 1

How to find pH when [H+] is known?

Answer 1

pH = -log[H+]

Question 2

How to find [H+] when given pH?

Answer 2

[H+] = 10^-pH

Question 3

How to find Kw in aqueous solutions?

Answer 3

Kw = [H+] x [OH-]

Question 4

How to find Ka when a weak acid is in an aqueous solution?

Answer 4

Ka = ([H+] x [A-]) / [HA]

Question 5

How to get pKa from Ka?

Answer 5

pKa = -logKa

Question 6

What is [HA]?

Answer 6

Concentration of acid

Question 7

What is [H+]?

Answer 7

Concentration of Hydrogen ions

Question 8

What is [A-]?

Answer 8

Concentration of conjugate base

Question 9

How to get pH of a strong acid?

Answer 9

pH = -log[HA]

This is because [HA] = [H+] as it can fully dissociate

Question 10

What is a Brønsted-Lowry acid?

Answer 10

A species that dissociates in aqueous solutions to produce H+ ions

Question 11

What is a Brønsted-Lowry alkali?

Answer 11

A species that dissociates in an aqueous solution to produce OH- ions

Question 12

What is a buffer?

Answer 12

A solution that can minimise changes to pH when small amounts of acid or base are added

Question 13

What happens when acid is added to a buffer?

Answer 13

• H+ conc increases
• H+ reacts with A-, forming more HA
• Equilibrium shifts to the left

Question 14

What happens when alkali is added to a buffer?

Answer 14

• OH- conc increases
• H+ reacts with OH- to form water
• HA dissociates to replace used H+, shifting equilibrium to the right